The sophistication and complexity of the electrical power grid has grown to include electricity meters that incorporate timing functions for billing metrics. Timing functions provide greater precision for consumers and providers by allowing increased ability to manage costs. For example, timing functionality is useful in “time-of-use” metering where the rate for energy can change depending on the time of day the energy is used.
Meters employing time-of-use metering employ a real time clock that is often based on a precision timing crystal. In some applications the precision timing crystal is a tuning fork style quartz crystal oscillator. The frequency of this crystal oscillator is a function of temperature. A temperature sensor is sometimes used to determine a correction factor for keeping the real time clock accurate.
Temperature readings from these sensors, however, do not directly measure the temperature of the crystal oscillator, and correction factors based on these measurements can be inaccurate and introduce compensation errors. There are industry standards for accuracy of the real time clock in utility meters. In particular, ANSI C12.1-2001 requirements for real time clock accuracy are two minutes per week or 200 ppm over a temperature range of 30° C. to 70° C. Some utilities require greater accuracies such as one minute per month or 23 ppm at temperatures of 30° C. and 40° C.
As industry standards for clock accuracy and variation across temperature become increasingly tighter, real time clock accuracy becomes an ever more important competitive feature and market differentiator for electric meter real time clocks. Previous solutions, that attempted to provide greater accuracy in identifying accurate correction factors, include adding a time delay to the temperature measurement before it is used to compensate the real time clock. Adding a time delay can provide a more accurate correction factor than an uncompensated temperature measurement; however, a time delay is an incomplete solution as it introduces compensation errors when ambient temperature shifts are rapid.
Solutions have been long sought but prior developments have not taught or suggested any complete solutions, and solutions to these problems have long eluded those skilled in the art. Thus there remains a considerable need for devices and methods that can provide accurate temperature correction factors for real time clocks.